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New Passenger Car Supplemental Category On the Horizon

The American Petroleum Institute has been working for many months on a proposed ‘Supplemental’ category to bridge the current SN specification to the completely new API GF-6 class that is already in being written. This proposed supplemental category is being developed at the request of automobile manufacturers to address a growing issue known as Low-Speed Pre-Ignition (LSPI).

The initial vote amongst manufacturers took place last August and has been on the fast track even since in an effort to quickly combat the LSPI issue occurring in turbocharged engines.

What is Low-Speed Pre-Ignition (LSPI)?

Low-Speed Pre-Ignition can occur in today’s smaller displacement turbocharged engines when rapid acceleration takes place at slower speeds, resulting in a quick increase in boost pressure. Known in chemistry terms as stochastic pre-ignition, the condition takes place when droplets of fuel and oil form in the combustion chamber which then ignite in advance of the time chamber sparking. This can lead to abnormal and sometimes uncontrollable combustion which can cause engine pressures to spike and inflict potentially serious and cost damage to the engine.

How Did We Get Here?

As federally-mandated improvements to fuel economy, emissions and overall performance continue to challenge auto makers at every turn, many have shifted their efforts to building smaller displacement engines that will still deliver the performance of their larger predecessors while still reducing CO2 output and bettering fuel economy.

Fuel economy alone is a major factor in this manufacturing shift all by itself. Federal mandates for model year 2016 passenger car (gasoline) engines have an overall average of 35.5 mpg. Fast forward to 2025 and that number jumps to 54.5 mpg, 53.5% increase.

Early models of this smaller generation of engines gave up a lot in performance (power) so turbochargers were added to boost pressure. Add in TGTI (Turbo Gasoline Direct Injection) technology and the percentage of units on the road subject to potential LSPI grew rapidly.

The Challenge

As more and more smaller displacement boosted engines roll off of assembly lines, the greater the risk to car owners and potentially expensive repairs lurk over their shoulders. The API’s working group for the proposed SN Plus category continue to face challengers surrounding existing test methods/sequences and how the new category testing can be harmonized. Manufacturers also face hurdles in that their ability to meet ever-increasing fuel economy and emissions standards is hampered without a remedy to LPSI (i.e. API SN Plus).

The panel met most recently on January 11th and are still hammering out the best rules for LSPI protection. Optimistic observers have expressed confidence that final comprehensive approval could take place with the next month, leading to a potential May 1 approval date which has been the wish since the beginning. Check back again for continuing updates on facets of this new category

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